Randomized Trial of Postoperative Radiation Therapy After Wide Excision of Neurotropic Melanoma of the Head and Neck (RTN2 Trial 01.09).

Background: Cutaneous neurotropic melanoma (NM) of the head and neck (H&N) is prone to local relapse, possibly due to difficulties widely excising the tumor. This trial assessed radiation therapy (RT) to the primary site after local excision.

Methods: Participants from 15 international centers were randomized to observation or RT. The participants were required to have microscopically negative excision margins 5 mm wide or wider and no evidence of disease elsewhere. The primary outcome was time to local relapse. The secondary outcomes included time to any recurrence, overall survival (OS), and toxicity.

Results: The trial ceased prematurely due to slow recruitment and the COVID-19 pandemic. During 2009-2020, 50 participants were randomized: 23 to observation and 27 to RT. The most common NM subsites were scalp (32%), midface (22%), and lip (20%). The median depth of invasion was 5 mm, and desmoplasia observed in 69%. The median duration from randomization to last contact was 4.8 years. Four participants (8%) experienced local relapse as a first recurrence during the study period: 3 in the observation arm and 1 in the RT arm (hazard ratio [HR] 0.29; 95% confidence interval [CI] 0.03-2.76; p = 0.279). No statistically significant difference in time to any relapse or OS was observed. More than 6 months after randomization, grade 3 or greater toxicity was experienced by 10% of the participants in the observation arm and 12.5% of the participants in the RT arm of the study.

Conclusion: Due to low accrual, the role of adjuvant RT for cutaneous NM of the H&N excised with microscopically negative margins 5 mm wide or wider remains undefined. Its routine use cannot be recommended. Local relapse might be less common than previously anticipated based on retrospective reports.